1. Field of the Invention
The present invention relates to a method for fabricating a conductive paste. According to the present method, the conductivity of the conductive paste can be significantly improved after a sintering process. 2. Description of Related Art
Conductive paste composed of a resin and a plurality of conductive particles is an adhesive agent having electrical conductivity after curing or drying, in which the conductive particles in collaborate with resin form a conductive path which can be applied in the fabrication of electronic devices. Owing to the excellent conductivity and the adhesive capability of the conductive paste, it is a promising material to replace the conventional solder so as to improve the productivity of the electronic devices and to apply to the materials with poor heat resistance or unable to be soldered.
The conductive paste usually used in the fabrication of micro-device, such as an integrated circuit, a light-emitting diode chip, or a printed circuit. In addition, it can also be applied to the communication systems, the vehicle industries and the medical equipment, which are fabricated by using the traditional solder. Further, for example, in the biomedical field, the conductive paste can also be applied to the blood glucose meter to enhance its functions.
The quality of the conductive paste is determined by the fabricating process and the composition thereof, for example, the uniformity of the dispersion of the conductive particles in the medium and the presence of generated bubbles in the conductive paste, and the baking temperature in the fabricating procedures. Therefore, the sintered conductive paste with poor quality shows high current resistant, which may induce degradation of the device and causing deterioration of the instruments and facilities, as a result, restricting the application of the paste.
Polyaniline is a conjugated conductive polymer with good processability and low density. Similar to other conductive polymers, the polyaniline also has high chemical stability, and the conductivity thereof can be adjusted by varying the processing parameters during polymerization. In 1982, the conductivity of the synthesized intrinsic polyaniline is only 10−11 S/cm, and it was increased to 10 S/cm, proposed by MacDiarmid et al., by doping a protonated acid with an oxidant therein. Although the conductivity of the polyaniline was improved, the solubility of the polyaniline is still too low to be used widely. Recently, it has found that the doped-polyaniline shows great improved stability, and therefore it can be used as an electromagnetic shielding material, an electrode for secondary battery, a heat resistant material, and a solar cell material, etc. Despite the improved solubility of the doped-polyaniline comparing to the intrinsic polyaniline, further improvement of the solubility of the polyaniline is still a critical issue to broaden the applications thereof.
In addition, during the sintering process of the polyaniline-based conductive paste, the water molecules and the dopant adsorbed in the polyaniline chain may be removed, resulting in the de-doping effect and decreasing the conductivity thereof.
Therefore, it is desirable to solve the aforementioned problems to provide better conductive paste having excellent conductivity.